With reference to FIG. 9, an operation in which a mobile station UE performs handover from a “cell#1 (Source cell)” to a “cell#2 (Target cell)” in a mobile communication system of a conventional LTE (Long Term Evolution) scheme is described.
As shown in FIG. 9, in step S2001, the mobile station UE sends an “RRC Measurement Report” to a radio base station eNB#1 that manages the cell#1.
In step S2002, the radio base station eNB#1 sends “HO Preparation” including “first security information” to a radio base station eNB#2 that manages the cell#2.
The “first security information” may be a security key applied to a communication between a mobile communication system including the cell#1 and the cell#2 and the mobile station UE, or may also be “secret information (shared secret)” calculated based on a certain rule previously determined between the mobile communication system including the cell#1 and the cell#2 and the mobile station UE.
In step S 2003, the radio base station eNB#2 sends “HO Preparation Ack” including “new C-RNTI” which is identification information of the mobile station UE in the cell #2, to the radio base station eNB#1.
In step S2004, the radio base station eNB#1 sends “RRC Reconfiguration (HO Command)” including “new C-RNTI” to the mobile station UE.
In step S2005, the mobile station UE sends “HARQ Ack” to notify the successful reception of “RRC Reconfiguration (HO Command)” in an MAC layer (layer 2) to the radio base station eNB#1.
In step S2006, the mobile station UE moves to the cell#2 instructed by the “RRC Reconfiguration (HO Command)” and establishes a downlink synchronization for the cell#2.
In step S2007, the mobile station UE sends “Dedicated RA Preamble (individual random access preamble)” or “Common RA Preamble (common random access preamble)” to the radio base station eNB#2 via RACH (Random Access Channel).
In step S2008, the radio base station eNB#2 sends “RA Response” to the mobile station UE. An uplink resource that should be used in a next step S2009 is assigned by the “RA Response”.
In step S2009, the mobile station UE sends “RRC Reconfiguration Complete (HO Complete)” including “second security information” by using the uplink resource assigned by “RA Response”, to the radio base station eNB#2.
In step S2010, the radio base station eNB#2 executes a verification process on the mobile station UE by using “second security information” included in the “first security information” and the “RRC Reconfiguration Complete (HO Complete)” notified by the radio base station eNB#1.
In step S2011, the radio base station eNB#2 sends “HARQ Ack” to notify the successful reception of “RRC Reconfiguration Complete (HO Complete)” in the MAC layer (layer 2), to the mobile station UE.
In step S2012, the radio base station eNB#2 sends “Path Switch” to a mobile switching machine MME.
In step S2013, the radio base station eNB#2 sends scheduling information to the mobile station UE by using “PDCCH (Physical Downlink Control Channel” that uses “new C-RNTI”, when data addressed to the mobile station UE is generated.
In step S2014, the radio base station eNB#2 sends data (U-Plane Data) addressed to the mobile station UE to the mobile station UE by using a downlink resource assigned by the scheduling information.
Alternatively, the mobile station UE, in step S2014, sends the data (U-Plane Data) addressed to the cell#2 to the radio base station eNB#2 by using an uplink resource assigned by the scheduling information.
In step S2015, the radio base station eNB#2 sends “RLC Status” that is transmission acknowledgement information of an RLC layer, to the mobile station UE.
In step S2016, the radio base station eNB#2 sends “Release Resource” to the radio base station eNB#1.
However, in the mobile communication system of a conventional LTE scheme, as shown in FIG. 10, since the “PCI (Physical Cell ID)”, which is the identification information to identify each cell, is configured in such a way that it is repeatedly assigned to a plurality of cells which are not in the vicinity of each other, there can be a case of (PCI Confusion) where a cell (for example, cell#3) assumed by the mobile station UE as the cell#2(Target cell)” and a cell (for example, cell#2) assumed by the radio base station eNB#1 as the “cell#2(Target cell)” are different.
There is a problem that if the mobile station UE performs handover to the cell#3 not intended from the cell#1, then the mobile station UE that has erroneously moved thereto by the handover receives the PDCCH information addressed to another mobile station UE as if this information was addressed to the mobile station UE if another mobile station UE using “C-RNTI” identical to “new C-RNTI” already existed in the cell#3, and as a result, the mobile station UE receives the data by using the downlink resource assigned by PDCCH or transmits the data by using the uplink resource assigned by PDCCH.
In particular, there is a problem that when the mobile station UE transmits HARQ Ack to downlink data or uplink data, communication by another mobile station UE is prevented.
There is a high possibility that such a problem becomes evident when, in particular, there are a number of small base stations such as a femto radio base station, a home radio base station, and a radio base station that manages CSG (closed subscriber cell).
Moreover, there is a possibility that such a problem becomes evident when a self-setting function or self-optimization function that selects and sets the “PCI (Physical Cell ID)” autonomously in each cell is installed.